1. Field of the Invention
The present invention relates to a disc apparatus and in particular relates to a disc apparatus for reproducing data from a recording disc having data recorded thereon in a ZCAV (Zoned Constant Angular Velocity)-type system.
2. Related Art
With reference to FIG. 1, a structure of a reproducing unit in an optical disc apparatus in the related art will now be described. An interface unit 36 includes, for example, a common SCSI interface. The unit 36 receives various instructions coming from outside of the apparatus and sends relevant predetermined instructions to various units in the apparatus. How data is read out from an optical disc 31 will now be described.
If logical reading-out instructions come to the interface unit 36 from the outside, the unit 36 converts logical address data included in the coming instructions into physical address data for recording areas in the disc 31. The thus obtained physical address data is used by the unit 36 to produce seek instructions for seeking a recording area in the disc 31 having a relevant target address. The seek instructions are sent to a servo unit 35 in a disc driving system of the apparatus. The servo unit 35 drives the disc 31 through a spindle motor 32 and, according to the seek instructions, moves a pick-up 33 to the recording area in the disc 31 having the target address.
The interface unit 36 further sends reading instructions to a read-out signal processing unit 37. The unit 37 receives an RF (radio frequency) read-out signal from the pick-up 33 and obtains relevant physical address data and other read-out data from the RF read-out signal. The thus obtained address data and other read-out data is sent to the interface unit 36 from the processing unit 37. The interface unit 36 determines whether or not the physical address data sent from the processing unit 37 is identical to the physical address data obtained as a result from converting the logical address data sent from the outside. That is, the interface unit 36 determines whether or not the address which the pick-up has accessed is identical to the above target address. If the interface unit 36 determines that the address which the pick-up has accessed is identical to the above target address, the unit 36 receives the above-mentioned other read-out data from the processing unit 37 and outputs the data to the outside of the apparatus. The above-mentioned other read-out data includes data which a user actually needs.
With reference to FIGS. 2 and 3, a sector format for a magneto-optical disc and various parts included in a sector having the sector format will now be generally described. A sector mark SM is located at the head of a pre-format part and has properties such that the sector mark SM can be detected even from read-out data in an asynchronous state. The data in an asynchronous state is data from which synchronization clock pulses have not been extracted and thus it is not possible to use the synchronization clock pulses to detect the sector mark SM or the like from the asynchronous data. The above properties of the sector mark SM may include those that, for example, a mark length of the mark is especially long and signal output obtainable from the mark is larger than those obtainable from other parts. Thus, it is possible to distinguish the sector mark SM from the other parts, that is, the address part, flag part, and data part.
Address marks AM1, AM2 and AM3 are located in the pre-format part behind the sector mark SM as shown in FIG. 2. The address marks have properties such that the marks can be detected only from read-out data in a synchronous state. In the synchronous state, since a synchronization clock pulses have been extracted from the read-out data, the synchronization clock pulses can be used to detect the marks from the read-out data. The term `read-out data in the synchronous state will be referred to as `synchronous data` hereinafter. The synchronous data and synchronization clock pulses are output by a PLL unit which will be described later.
The three address parts ID1, ID2 and ID3 are located subsequent to the address marks AM1, AM2 and AM3, respectively, as shown in FIG. 2. These address parts ID1, ID2 and ID3 have same address data previously recorded and the address data includes a track number and a sector number. The address parts ID1, ID2 and ID3 further have numbers indicating orders of the relevant address parts in the sector. Further, the pre-format part has data patterns VFO1, VFO2 and VFO3 recorded as shown in FIG. 2 and the data patterns are used for a PLL unit's locking operation.
A flag part, a data part to have user data recorded, and a buffer part are located subsequent to the pre-format part. A magneto-optical disc apparatus first reads the pre-format part so as to obtain the address data and, after that, obtains relevant read-out data.
With reference to FIG. 4, a structure of the read-out signal processing unit using a CAV (Constant Angular Velocity)-type system in the related art will now be described. The read-out signal obtained via the optical pick-up 33 is received by wave shaping units 41 and 42 which then convert the read-out signal in an analog form into the signal in a digital form. The signal in the digital form can be easily processed by various units to process the read-out signal output from the units 41 and 42.
A reading-out timing signal producing unit 46 receives the read-out signal carrying read-out data in the asynchronous state from the wave shaping unit 41. The term `read-out data in the asynchronous state` will be referred to as `asynchronous data` hereinafter. The reading-out timing signal producing unit 46 further receives reference clock pulses to be used for obtaining read-out data to be output to the interface unit 36. The reference clock pulses are supplied by a reference-clock-pulse generating unit 43.
The reading-out timing signal producing unit 46 detects the sector mark SM from the received asynchronous data and outputs a corresponding sector-mark detection signal to an address demodulating unit 47. The producing unit 46 produces an address-mark detecting-timing signal for detecting the address marks AM and outputs the signal to the address demodulating unit 47.
The reading-out timing signal producing unit 46 further produces various reading-out timing signals indicating data demodulating timing and sends the signals to a data demodulating unit 45. The producing unit 46 supplies a locking timing gate signal to the PLL unit 44 which then uses the signal for VFO detection by gating a signal carrying the synchronous data.
The PLL unit 44 receives the reference clock pulses and locking timing gate signal, each signal having frequency approximately identical to a reproducing frequency. The reproducing frequency is a frequency suitable to a recording frequency in which data has been recorded in a recording disc. That is, the data has been recorded in the recording disc in synchronization with clock pulses having the recording frequency. Using the reference clock pulses and locking timing gate signal, the PLL unit 44 produces the synchronous data and synchronization clock pulses from the asynchronous data sent from the wave shaping unit 42. The synchronous data and synchronization clock pulses are sent to the address demodulating unit 47 and data demodulating unit 45.
The address demodulating unit 47 demodulates the address data from the synchronous data. If the unit 47 has properly demodulated the address data, the unit 47 sends timing correcting pulses to the reading-out timing signal producing unit 46 which uses the timing correcting pulses to correct timing indicated by the address-mark detecting timing signal and reading-out timing signals.
The data demodulating unit 45 demodulates reading-out data to be supplied to the interface unit 36 from the synchronous data in response to the reading-out instructions sent from the interface unit 36. The demodulation is carried out in synchronization with the timing indicated by the reading-out timing signals.
With reference to FIG. 5, details of the reading-out timing signal producing unit 46 and address demodulating unit 47 will now be described. The reading-out timing signal producing unit 46 includes a sector-mark detecting unit 51, a sector-length counter 52, a preset unit 60 and a gate-span setting unit 61.
The address demodulating unit 47 includes an address-mark detecting gate producing unit 55, an address-mark detecting unit 56, an address-data demodulating gate production unit 57, an address-data demodulating unit 58 and an address-data determining unit 59.
The sector-mark detecting unit 51 detects a sector mark SM indicating the beginning of a sector from asynchronous data read out from a recording disc and outputs a sector-mark detection pulse when the unit 51 detects the rear end of the detected sector mark SM. The sector-mark detection is achieved by detecting a particular pattern of the sector mark from the asynchronous data, for example, sampled in synchronization with system clock pulses having a frequency quite a lot higher than the reproducing frequency.
Data lengths of each part of all the parts included in a sector according to the standard sector format shown in FIG. 2 are previously stored in the sector-length counter 52. After the sector mark has been detected, the sector-length counter 52 counts the reference clock pulses according to the stored data lengths so as to output address-mark detecting timing pulses and various reading-out timing pulses corresponding to the data lengths of the parts of a sector. The counter 52 is a loop-type counter which automatically starts the same counting from an initial counting value `0` after completing the counting for all the data lengths of a sector.
The preset unit 60 receives the sector-mark detection pulse from the sector-mark detecting unit 51 and the timing correcting pulses from the address demodulating unit 47. When the sector detection pulse has been received or when the timing correction pulses are received, the preset unit 60 supplies timing correcting data to the sector-length counter 52 so as to set appropriate numbers to the counter 52. That is, whether or not the counter 52 has already counted a number, the preset unit sets a certain count number to the counter regardless of the already counted number if it is present in the counter. Thus, the counter 52 has the certain count number as if the certain count number were obtained as a result of the counter 52 having counted. Thus, the counter 52 counts from the thus set certain count number. Thus, the counter 52 is in synchronization with the actual coming timing of the parts of the sector shown in FIG. 2.
The address-mark detecting pulses output by the sector-length counter 52 have to be in synchronization with the synchronous data so as to effectively extract the address marks from the synchronous data. Time difference is inevitably present between the asynchronous data supplied to the sector-mark detecting unit 51 and the synchronous data supplied by the PLL unit 44, due to properties of circuits through which the data passes. Specifically, the synchronous data is delayed from the asynchronous data by several bits.
According to the above-mentioned time difference, the preset unit 60 supplies timing correcting data together with a loading signal to the sector-length counter 52 when the sector-mark detection pulse has been received. A count number corresponding to the timing correcting data including an offset value corresponding to the above-mentioned time difference is set to the counter 52 so that a current count number of the sector-length counter 52 is appropriately corrected. As a result, the timing pulses generated by the sector-length counter 52 are synchronized with the synchronous data.
If the sector-mark detecting unit 51 has failed in detecting of the sector mark, the preset unit 60 supplies the timing correcting data together with the loading signal to the sector-length counter 52 when the timing correcting pulses have been supplied to the preset unit 60. A count number corresponding to the timing correcting data is preset to the sector-length counter 52 so that the current count number of the sector-length counter 52 is appropriately corrected according to the above-mentioned time difference. Thus, even if the sector-mark detection has been missed, the timing correcting pulses can be used, instead of the sector-mark detection pulse, to correct the generation timing of the timing pulses supplied by the sector-length counter 52 according to the above-mentioned time difference between the synchronous data and asynchronous data.
The gate-span setting unit 61 generates a gate-span setting signal to be supplied to the address-mark detecting gate producing unit 55. In the generation of the gate-span setting signal, the unit 61 uses the sector-mark detection signal and a current counted value of the sector-length counter 52. The gate-span setting signal instructs as to whether the necessary and minimum first time span or a second time span longer than the first time span is used as a time span of an address-mark detecting gate period which is to be defined by address-mark detecting gate producing unit 55.
The gate-span setting unit 61 produces the gate-span setting signal instructing the first time span when the sector-mark detection pulse has been received. If the above-mentioned counted value has reached a reference value, the unit 61 produces the gate-span setting signal instructing the second time span. This reference value is a counted value of the sector-length counter 52 corresponding to the rear end of all the address-mark detecting gate periods defined For a sector. Thus, the longer second time span is used as a time span of the address-mark detecting gate period when reading out of a subsequent sector is begun.
The address-mark detecting gate producing unit 55 receives the address-mark detecting timing pulses, indicating the beginning of the address marks present in the synchronous data, from the sector-length counter 52 so as to produce signals indicating the corresponding address-mark detecting gate periods to be sent to the address-mark detecting unit 56. The address-mark detecting unit 56 detects the address marks from the synchronous data in synchronization with the synchronization clock pulses during the address-mark detecting gate periods. The detecting unit 56 outputs address-mark detection pulses when the ends of the address marks have been detected.
The address-data demodulating gate producing unit 57 produces address-data demodulating gate periods using, as a reference time, the time when the address-mark detection pulses have been received. Signals indicating the address-data demodulating gate periods are sent to the address-data demodulating unit 58 which includes a 2-7 demodulating unit and a CRC checking unit and demodulates address data present during the address-data demodulating gate periods.
The address-data determining unit 59 determines what numbers orders of the address data sent from the address-data demodulating unit 58 in the sector are. In accordance with the determined numbers, the unit 59 produces any one of timing correcting pulses (1), (2) and (3) to be sent to the preset unit 60. That is, if a determined number of the above-mentioned determining numbers indicates that relevant address data is address data written in the first address part ID1 shown in FIG. 2, the unit 59 produces the timing correcting pulse (1) instructing the beginning of the VF02. Similarly, if a determined number of the above-mentioned determining numbers indicates that relevant address data is address data written in the second address part ID2, the unit 59 produces the timing correcting pulse (2) instructing the beginning of the VFO3. If a determined number of the above-mentioned determining numbers indicates that relevant address data is address data written in the third address part ID3, the unit 59 produces the timing correcting pulse (3) instructing the beginning of the flag part.
Thus, the preset unit 60, only if the sector-mark detection has been missed, presets a count number corresponding to the timing correcting data, to the sector-length counter 52, corresponding to the above-described timing correcting pulses (1), (2) and (3) when the timing correcting pulses have been supplied. Thus, the count number corresponding to the timing correcting data is set to the sector-length counter 52 so that the current count number of the counter 52 is appropriately corrected according to the time difference between the synchronous data and asynchronous data.
Operation in a case when the address mark AM1 shown in FIG. 2 is detected will now be described. As described above, the sector-length counter 52 receives the timing correcting data, for correcting the count number in the counter 52 according to the time difference between the synchronous data and asynchronous data, when the sector-mark detection pulse has been received. The counter 52 thus counts the reference clock pulses for an offset corresponding to the time difference and then for the data length of the VFO1 since the rear end of the sector mark SM was detected. As a result, the counter 52 generates the address-mark detecting timing pulse for the address mark AM1 when the above counting has been completed, the pulse thus instructing the beginning of the address mark AM1 in the synchronous data.
The address-mark detecting gate producing unit 55 receives the thus generated address-mark detecting timing pulse for AM1 and thus produces the address-mark detecting gate period for AM1 to be sent to the address-mark detecting unit 56. The gate producing unit 55 uses the gate-span setting signal, specifying the above-mentioned first time span, sent from the gate-span setting unit 61 so that the produced address-mark detecting gate period has the first time span.
The address-mark detecting unit 56, during the time span of the thus produced address-mark detecting gate period for AM1, detects the address mark AM1 from the synchronous data in synchronization with the synchronization clock pulses. The unit 56 outputs the address-mark detection pulse for AM1 indicating the rear end of the address mark AM1.
The address-data demodulating gate producing unit 57 produces the address-data demodulating gate period for the address data including data written in the address part ID1 using, as a reference time, the time the address-mark detecting pulse for AM1 has been received. A signal indicating the produced gate period is sent to the address-data demodulating unit 58 which, during the time span of the sent gate period, demodulates the address data written in the address part ID1.
The address-data determining unit 59, using the address data of the address part ID1 sent from the demodulating unit 58, determines that the thus sent address data is data in the first address part in the sector. As a result, the determining unit 59 produces the above-mentioned timing correcting pulse (1) instructing the beginning of the VFO2 in the synchronous data and sends the pulse to the preset unit 60.
Operation in cases where the address marks AM2 and AM3 are detected will now be described. After the timing correcting pulse (1) has been thus produced, the sector-length counter 52 produces the address-mark detecting timing pulse for AM2 and address-mark detecting timing pulse for AM3 to be sent to the address-mark detecting gate producing unit 55. The address mark detecting unit 56, using the thus produced pulses for AM2 and AM3, detects the address marks AM2 and AM3, and produces the corresponding address-mark detection pulse for AM2 and that for AM3, similarly to the case where the address mark AM1 is detected.
The address-data determining unit 59 receives the address data of the second address part ID2 subsequent to the address mark AM2 and thus produces the timing correcting pulse (2) instructing the beginning of the VFO3. The address-data determining unit 59 receives the address data of the third address part ID3 subsequent to the address mark AM3 and thus produces the timing correcting pulse (3) instructing the beginning of the flag part.
The sector-length counter 52, after producing the address-mark detecting timing pulse for AM3, produces the various reading-out timing pulses such as a flag-part beginning timing pulse, a data-part beginning timing pulse, a buffer-part beginning timing pulse, and so forth to be sent to the data demodulating unit 45.
Since the sector-length counter 52 is the loop-type counter as described above, even if detection of the sector mark in a current sector fails, as long as an address mark of the address marks AM1, AM2 and AM3 was properly detected in an antecedent sector, the sector-length counter 52 produces the address-mark detecting timing pulses for the current sector in approximately proper timing. This is because, as described above, the counter 52 acting as the loop-type counter automatically begins a counting action counting the reference clock pulses from the initial counting value `0` after completing the counting for all the data lengths of the antecedent sector. Further, in this case, since no sector-mark detection pulse has been supplied to the gate-span setting unit 61, the unit 61 produces the gate-span setting signal specifying the above-mentioned second time span for a relevant gate period. Since the second time span is longer than the necessary and minimum first time span as mentioned above, it is likely that an address mark of the marks AM1, AM2 and AM3 can be detected from the current sector although the sector mark could not be detected.
If the sector mark could not be detected and an address mark of the address marks AM1, AM2 and AM3 could be detected, the timing correcting pulses corresponding to the detected address mark are produced so as to be sent to the preset unit 60. Then, the sector-length counter 52 thus has the sent timing correcting pulses preset thereto by the preset unit 60 so that a current count number of the counter 52 is corrected. Thus, the counter 52 can generates the timing pulses in corrected timing.
If the detection of the sector mark has been missed, a time span of the address-mark detecting timing gate period is kept at the long second time span even after the address mark has been detected. Thus, since the time span of the gate period is long, subsequent address marks are likely to be detected.
If the sector mark has been properly detected, the count number is corrected in the sector-length counter 52 according to the time difference between the synchronous data and asynchronous data only when the sector mark has been detected. The count number is not corrected in the sector-length counter 52 according to the time difference by the timing correcting pulses produced due to the address-mark detection.
Such a time difference between the synchronous data and asynchronous data includes an independent component, independent of the above-mentioned reproducing frequency, approximately the same as the frequency of the reference clock pulses and a dependent component varying depending on the reproducing frequency. The above independent component of the time difference occurs due mainly to the wave shaping unit 52. The above dependent component is time delay having time for one period of the reference clock pulses and occurs in the PLL unit 44.
In a CAV-type magneto-optical disc recording/reproducing system, time-axis data-recording densities in a recording disc are uniform over different recording zones classified along a radius of the disc. The condition where the time-axis data-recording densities are uniform is referred to as a condition where, as long as the disc is rotated at a constant angular velocity, recording densities seen via a pick-up accessing the disc are apparently uniform. Such condition can be achieved as a result of the actual recording densities being closer in the recording zones near the center of the disc. In this system, reference clock pulses such as described above have to have a single frequency corresponding to the reproducing frequency for all the recording zones. Thus, the time difference between the synchronous data and asynchronous data is also constant over the recording zones. As a result, the timing correcting data produced by the preset unit 60 can be produced according only to this constant time difference.
Instead of the above-mentioned CAV-type system, a ZCAV-type magneto-optical disc recording/reproducing system has recently been proposed. In the ZCAV system, time-axis recording densities are different over different recording zones classified along a radius of the disc. Specifically, the time-axis recording densities are closer as the zones are away from the center of the disc. Thus, actual recording densities (not the time-axis apparent recording densities but recording densities seen while the disc is static) are made uniform over the zones. As a result, it is possible to make actual data recording densities in the disc higher. In this system, the different reproducing frequencies are necessary to reproduce data from the recording disc so that the reference clock pulses have to have different frequencies over the recording zones. Thus, the time difference between the synchronous data and asynchronous data is different among the recording zones. As a result, the timing correcting data produced by the preset unit 60 can be produced according to those different time differences.
As mentioned above, it is assumed in the CAV-type system that the time difference between the synchronous data and asynchronous data is fixed. Thus, the timing correcting data produced by the preset unit 60 uses the fixed time difference for the all the recording zones. Thus, if the above-described read-out signal processing unit 37 for the CAV-type system were used for the ZCAV system, the thus generated address-mark detecting gate periods might not have proper generation timing corresponding to actual address-mark positions in the disc. Thus, it might be likely that the address marks could not be properly detected.
By making earlier of the generation timing of the address-mark detecting gate periods and extending the time spans of the gate periods, missing of the address-mark detection can be prevented. However, in this modification, erroneous address-mark detection is likely to occur due to the extended gate-period time-spans.